1. Field of the Invention
The present invention relates to a medical imaging apparatus in which an imaging portion is movable to a position of a subject by way of a weight balance mechanism.
2. Description of the Related Art
An imaging apparatus in which an imaging portion is vertically movably supported so that it can be arranged in a desired posture typically employs a manual movement mechanism to keep a weight balance using a mechanism which couples the imaging portion with a weight having an equivalent weight to that of the imaging portion by a wire or the like, or that uses a balance control mechanism with a spring force. Such an imaging apparatus that employs the weight balance mechanism is applied to, for example, a radiographic imaging apparatus supported with a vertical stand or a C-arm.
FIG. 6 shows a supporting base of a typical radiographic imaging apparatus. A column 2 is vertically provided on a pedestal 1. A pulley 4 with a wire 3 wounded thereon is hung from an upper portion of the column 2. A first end of the wire 3 is connected to a weight 5, and a second end thereof is connected to a holder 7 that fixes an imaging portion 6. When a handle 8 provided in a side surface of the holder 7 is manually operated, the imaging portion 6 is vertically moved in a Z1 direction along the column 2 via the holder 7. The weight 5 has a weight which is balanced with the total weight of the imaging portion 6 and the holder 7. The weight 5 is vertically movable in a Z2 direction while the weight balance is constantly kept in the column 2.
Japanese Patent Laid-Open No. 6-169904 discloses an adjustment mechanism for a weight balance during rotational movement of a C-arm. In the mechanism, an imaging portion is coupled with a weight having an equivalent weight to that of the imaging portion to hold the weight balance. In recent years, with a progress in semiconductor process technology, an apparatus for imaging a radiographic image with a semiconductor sensor has been developed. FIG. 7 is a conceptual diagram showing an imaging system that uses such a radiographic imaging apparatus. A radiographic imaging apparatus 11 includes therein a radiation sensor 12. A subject S is irradiated with radiation emitted from a radiation source 13 arranged behind the subject S. The radiation transmitted through the subject S is converted into visible light through a fluorescent member provided in the radiation sensor 12. The visible light converted through the fluorescent member is detected as an electric signal by photoelectric conversion elements arrayed in a two-dimensional grid form.
A controller 14 that controls the radiation sensor 12 for driving of reading and image transferring is connected to the radiographic imaging apparatus 11. The controller 14 performs image processing for an image output from the radiation sensor 12, and displays a radiographic image of the subject S on a monitor 15.
In this imaging system, an image can be observed instantly, unlike a radiographic image recording and reproducing system that reads an image in post processing. Further, in this imaging system, a detection panel is provided on a dedicated pedestal corresponding to a capturing mode such as standing, lying, or the like. The detection panel is selected according to what is needed.
Recently, a portable X-ray detector has been developed and used for capturing an image with the subject in a desired capturing posture. Japanese Patent Laid-Open No. 2005-470 suggests an X-ray imaging apparatus in which such a portable X-ray detector is used, the X-ray detector is fixed at a position facing an X-ray tube, and the X-ray detector is used in a manner separated from a supporting portion.
With the portable X-ray detector, positioning can be easily performed, and alignment with high precision can be rapidly performed. Also, since the X-ray detector is arranged at a desired position, an image can be captured by moving the apparatus in accordance with the position of a subject, which is not movable, to reduce the burden on the subject. That is, two capturing modes can be provided with a single apparatus. This increases convenience of use.
Hitherto, in such an imaging apparatus, an imaging portion is disposed on a dedicated supporting device corresponding to a capturing mode. However, in recent years, there have been provided an apparatus in which a portable imaging portion is used, and a single supporting device is commonly used for a plurality of such imaging portions; or an apparatus in which an imaging portion has to be detached or attached during installation or the like. Hence, a weight balance may be disrupted when the imaging portion is detached or attached. If the weight balance is disrupted, the posture of the imaging portion may be rapidly changed, and inhibition operations relating to a detachment or attachment position and a condition of a movable portion have to be manually performed.